<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <title>伸缩盒居中</title>
    <style>
        .outer {
            width: 1000px;
            height: 600px;
            background-color: #888;
            margin: 0 auto;
            display: flex;
            flex-wrap: wrap;

            /* 方案一 */
            /* justify-content: center; */
            /* align-items: center; */

          


        }

        .inner {
            width: 200px;
            height: 198px;
            border: 1px solid black;
            background-color: skyblue;

              /* 方案二 */
              margin: auto;
        }
       
    </style>
</head>

<body>
    <div class="outer">
        <div class="inner inner1">1</div>

    </div>

</body>

</html>